Melatonin has been shown to be effective in advancing the breeding season of the ewe when given either orally or by subcutaneous implantation. We have demonstrated that it is also effective when given as an intravaginal implant containing melatonin in silastic tubing. Such implants have the advantage that they are much easier to insert and remove than subcutaneous implants. Rate of implant loss is extremely low. The present abstract summarises the result of several experiments which have examined the effectiveness of melatonin implants when given at different times of year. Animals used were either Mule ewes or their Suffolk cross offspring. All were kept outside under normal management conditions. Groups of in ewes were given implants on either 12 April, 13 May, 18 July, or 21 December. Control ewes received empty implants. Blood samples were taken twice Weekkly for progesterone analysis to estimate the tire of onset of ovarian activity.